Seal structure for electric lamps and similar devices



Patented Oct. 15, 1946 SEAL STRUCTURE FOR ELECTRIC LAMPS AND SIMILAR DEVICES Eric Kettlewell, Kingsbury, London, England, assignor to General Electric Company, a corporation of New York Application March 30, 1944, Serial No. 528,660 In Great Britain April 3, 1942 7 Claims. 1

This invention relates to devices of the type comprising an envelope of quartz or similar refractory material and an electrode therein (with current lead connections to the exterior), which electrode would become overheated in ordinary operation if provision were not made for cooling it. This is especially the case with high pressure metal vapor discharge devices, such as mercury vapor lamps having an energy consumption of some to kW. or upward. 'In a high pressure discharge device operated on D. C., the electrode which thus tends to overheat is usually the anode. It is an aim of this invention to provide for bringing cooling fluid into eiiective cooling relation or thermal contact with an electrode that needs cooling.

.To provide conveniently for cooling the electrode by a stream or flow of cooling fluid (usually water or air), the electrode is attached to the inside 'of the envelope wall, and a coolin conduit is attached to the outside of the envelope wall so that the fluid therein covers an external wall area which in turn substantially covers 0r corresponds with the internal attachment or contact of the electrode as aforesaid. In the form of embodiment of the invention here illustrated and described, part of the electrode lies in a thinwalled vitreous refractory tube that forms part of the envelope wall and projects into one end of a surrounding larger external tube or conduit,

through whose other end a stream of coolant can be introduced and withdrawn. Instead of passing through the envelope wall right where the electrode is attached thereto, current leads to the electrode are shown as strip seal leads lying between the exterior of said larger tube (or of a yet larger tube surrounding it) and a surrounding vitreous structure internally sealed to the last-mentioned tube, and forming a portion of the envelope wall or associated therewith, the seal being conveniently .formed by heating, softening, and collapsing the structure in question upon the tube directly within it, and interfusing it therewith.

Other features and advantages of the invention will become apparent from the description of a species or form of embodiment.

The single figure of the drawing shows an axial exaggerate their thickness.

section through a portion of a discharge device envelope structure and associated parts which embody and exemplify the invention.

The discharge electrode in question is here shown as a tungsten rod I fitting as closely as possible into a quartz tube 2 that is closed at its outer end 3 and has its other end sealed into an aperture in a relatively thick quartz plate or disc 4 (whereof the tube 2 is thus in effect a portion) which closes the inner end of a quartz tube 5 that forms part of the discharge envelope wall. Thus the outward extending tube 2 affords a reverse internal pocket within a larger main reentrant external pocket formed by the inward extending tube 5. As illustrative dimensions, the electrode rod I may be 8 mm. in diameter, the wall of the tube 2 may be 1% mm. thick, the plate 4 may be 4 mm. thick, and the tube 5 may be some 20 mm. in internal diameter, with a wall about 4 mm. thick. Thin molybdenum strips 6 lie between the outer surface of the tube 5 and the surrounding quartz tube or sleeve structure l, which is ultimately heated and softened and so collapsed on the strips 6, 6 and the tube 5, and interfused with and sealed to the latter. For the sake of clearness as regards fabrication of the device, the drawing shows the bulb neck i and the tube 5 as separate parts, before being fused and sealed together, with slight clearance between them and between each of them and the two strips 6, 6. That these strips 6, fi-are not shown in section is consistent with their lying behind the plane of section represented in the drawing, as Well as with their being so thin that even the single lines representing them would At each end, each strip '6 is joined in the usual manner to stouter leads 8, 9. The leads 8 extend to the exterior of the device; the leads 9 are connected to the electrode l at points inside the envelope. An annular seal ID of quartz around the quartz sleeve l forms the junction of the parts shown with the rest of the envelope, not shown except fragmentarily. The sleeve 1 forms as it were a neck for the envelope or bulb.

, If this were all, and a coolant were introduced into the tube 5, the coolant might cool the upper part II of the tube-Which lies inside the envelope and forms a portion of its wall-suiiiciently to form an undesirable cold spot, where mercury would condense so that the desired pressure could not be maintained in the envelope. Accordingly, the (relatively thin) intermediate tube or conduit wall I2 is introduced between the tubes 5 and 2 and is spaced at an interval from each, with its inner end attached or sealed to the plate 4. For the above-indicated dimensions of the tubes 2 and 5, the tube l2 may be of about 12 mm. diameter. The coolant circulates within this tube l2 around the tube 2 and comes in contact with the latter and cools it, but it is separated from the part II of the outside envelope or pocket wall by the insulating space [3, so that it is out of contact with this wall and so does not produce a materially or excessively cooled wall area around the electrode l. Good thermal contact between the rod l and the tube 2 is nevertheless assured by the mercury that will condense in any interstices between them.

Th tube or wall [2 may be dispensed with by making the plate 4 sufficiently thick to hinder heat transferenc through it and attaching the annular envelope seal to the sleeve 1 substantially at the plane or level of the plate 4, as shown in dotted lines at [0, in other words, virtually attaching the seal It! to the rim of the plate. With this arrangement, the part II of the tube 5 lies outside the envelope and forms no portion of its wall, so that it does not matter for it to be cold.

In general, and as a practical matter, refractory envelope material similar to quartz is any highly silicious vitreous material which has a coefficient of expansion of not more substantially than 1.5 10 per degree centigrade, as compared with a corresponding coefiicient of expansion of 0.55 10 per degree centigrade for fused quartz o1 quartz glass itself.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The combination with a vitreous refractory envelope wall having an outward projecting vitreous portion affording an internal pocket, and a discharge electrode fitted into said pocket, of an external fluid conduit wall attached to said envelope wall around its said outward projecting portion, and means for circulating cooling fluid in the conduit in contact with said outward projecting wall portion to the inside of which said electrode is attached, thus cooling said electrode.

2'. The combination with a vitreous refractory envelope wall having an outward projecting relatively thin portion affording an internal pocket, with a relatively thick zone around said outward projecting portion, of a discharge electrode fitted into said pocket, an external fluid conduit wall attached to the thickened envelope wall zone at an interval around said outward projecting wall portion, and means for circulating cooling fluid in the conduit in contact with said outward projecting wall portion, thus cooling said electrode without producing an excessively cool envelope wall area around the electrode.

3. The combination with a vitreous refractory envelope wall having a reentrant portion affording a main pocket, with a relatively thin portion of the main pocket wall projecting outward into said main pocket and thus affording a reverse pocket, of a discharge electrode attached to the inside of said reverse pocket, and means for circulating cooling fluid in said main pocket in external contact with said reverse pocket, thus cooling said electrode.

4. The combination with a vitreous refractory envelope Wall having a reentrant portion affording a main pocket, and with a discharge electrode attached to the inner side of the bottom pocket wall, or a fluid conduit Wall attached to the outer side of the bottom pocket wall, within the pocket and around an external area of said bottom wall covering the internal attachment of said electrode thereto, and means for circulating cooling fluid in said conduit in contact with said area, but out of contact with the main pocket wall around the said conduit wall, thus cooling said electrode without producing a materially cooled envelope wall area around the electrode.

5. The combination with a vitreous refractory envelope wall having a reentrant portion affording a main pocket, with a relatively thin portion of the main pocket wall projecting outward into said main pocket and thus affording a reverse pocket, and with the main pocket wall around said reverse pocket relatively thick, of a discharge electrode fitted into said reverse pocket, a fluid conduit wall attached to the outer side of the thickened bottom main pocket wall at an interval around said reverse pocket, and means for circulating cooling fluid in said conduit around and in external contact with said reverse pocket, but out of contact with the main pocket wall around the said conduit wall, thus cooling said electrode without producing a materially cooled envelope wall area around the electrode.

6. The combination with a vitreous refractory envelope wall and a vitreous refractory tube sealed therethrough having an inner end wall with a portion projecting reversely outward into the tube and thus affording an internal pocket in said end wall, of a discharge electrode fitted into said pocket, current lead means extending inward in the thickness of the tubular wall to said electrode, and means for circulating cooling fluid around and in external contact with said outward projecting wall portion inside said other tube, thus cooling said electrode.

7. The combination with a vitreous refractory main envelope wall having an opening and a. sleeve portion around said opening, and a vitreous refractory tube extending through said sleeve portion inward beyond said main wall and having an inner end wall with a portion projecting reversely outward into the tube and thus affording an internal pocket in said end wall, of a discharge electrode fitted into said pocket, current lead means extending inward between said sleeve and tube to said electrode, said sleeve and tube having their inner and outer surfaces sealed together with said current lead means embedded in the another tube Within the tube aforesaid around the said pocket having its inner end sealed to the aforesaid inner end wall of the first-mentioned tube, and means for circulating cooling fluid around and in external contact with said outward projecting wall portion inside said other tube, thus cooling said electrode.

ERIC KEI'ILEWELL. 

